1. Field of the Invention
The present invention relates to a semiconductor pressure sensor for detecting a pressure such as, for example, the pressure in an intake manifold of an internal combustion engine, the internal pressure of a tank, etc
2. Description of the Related Art
As a general pressure sensing element, there has been known a semiconductor pressure sensor using a piezoresistive effect, for example.
Such a semiconductor pressure sensor is constructed as follows. That is, a seat with a diaphragm bonded thereto is arranged in a concave portion of a package, and a strain gauge formed on the diaphragm serves to catch, as a change in resistance, a strain or distortion of the diaphragm that is caused by a pressure difference between a medium or fluid to be measured and a vacuum chamber defined between the diaphragm and the seat, so that the change in resistance is output as an electric signal to the outside through leads, and the pressure of the fluid to be measured is thereby detected.
The diaphragm and the leads are electrically connected with each other through bonding wires, and the diaphragm and the bonding wires are covered with and protected by an electrically insulating protective resin material or portion so as to ensure the corrosion resistance and the electrical insulation thereof to the medium to be measured, but as such a resin material, there is used a relatively soft one such as for example a gel so as not to obstruct the strain or distortion deformation of the diaphragm.
However, minute gaps or clearances are formed in interfaces between the package and the leads which are formed integral with the package by means of insert molding, so when the diaphragm and the bonding wires are covered with the protective resin portion, air existing in the interfaces is released into the protective resin portion, as a result of which a stress is applied to the bonding wires, thereby causing a fear that the bonding wires might be damaged.
In order to prevent such a situation, a countermeasure is taken in which work to cover the protective resin portion is carried out under a vacuum atmosphere so as to reduce the amount of air confined or trapped in the interfaces, but even in this case, when the diaphragm is subjected to a negative pressure lower than the atmospheric pressure, the air existing in the minute gap expands as air bubbles to invade into the protective resin portion, whereby the protective resin portion and the bonding wires are stressed, and hence there was still a problem that the damage of the bonding wires might be caused.
Here, note that a similar problem was generated by the air that invaded from the outside of the package through small gaps.
As a means for solving such problems, for example, a semiconductor pressure sensor is described in a first patent document (Japanese patent application laid-open No. H11-304619 (FIG. 1)). That is, a concave portion side, lower portions of the bonding wires and the leads on the interfaces between the leads and the package are covered with a first relatively hard, insulating protective resin portion thereby to confine air in the interface, and the diaphragm and upper portions of the bonding wires are covered with a second relatively soft protective resin portion.
However, in the above-mentioned semiconductor pressure sensor, the bonding wires are covered with the first protective resin portion and the second protective resin portion which are different from each other in the coefficient of linear expansion and the elastic modulus, so a difference or variation in the stress or distortion of the first protective resin portion and the second protective resin portion caused by a temperature change or a pressure change acts on the bonding wires as a large force as it is. Accordingly, even in this case, there was a problem that the bonding wires might be damaged.